[CAUT] Thank you for Stability advice

[Keith Roberts]

Thank you very much, Ron.

KR

On Tue, Feb 9, 2010 at 12:09 PM, Ron Nossaman <rnossaman at cox.net> wrote:

> Keith Roberts wrote:
>
>> Gentlemen, excuse me for butting in,
>>  I think Ron also writes of bridge pins that push themselves out of the
>> bridge due to the way they were installed.
>>
>
> Not exactly. The point of zero relative movement between the pin and bridge
> tends to be at about the bottom of the cap, maybe 8mm down. The bridge cap
> rides the string up and down on the pin with humidity cycles. The bottom of
> the hole, meanwhile recedes from and approaches the bottom of the pin
> similarly. This is why bottoming pins in the hole doesn't do anything to
> "seat" the pins. The next humidity cycle will put them right back where they
> were. The pins don't advance out of the bridge farther than the bottom of
> the hole at the driest part of the cycle can directly push them.
>
>
>
> When a wear spot on the pin has developed, the pin could reduce the
>> pressure of the wire on the bridge as the pin gets squeezed out.
>>
>
> Not unless the dry cycle is the driest it's ever been, and the pin is
> extremely worn.
>
>
>
> As the humidity cycles, the job of setting it back in place has to be done
>> again.
>>
>
> Not so. By the time the flat spot has worn that deeply into the pin, the
> 15lb friction between the pin and string that I keep so hopefully mentioning
> will have crushed the notch edge below the line between the bridge top and
> capo. The string is still on the bridge, but the notch has been crushed
> below string plane.
>
>
>
> The pin would also become loose and setting it the first few times would
>> make the biggest difference.
>>
>
> Setting the pin is making use of that 15lbs of friction between the pin and
> string that I keep so hopefully mentioning, and pushing the string into the
> bridge with 15lbs of force, which is at least nominally equivalent to
> seating the string. There is no acoustic benefit to seating the pin.
>
> Turning the pin (as you suggested earlier) to get a fresh surface would
> eliminate any problems with the pin wear, but the existing damage to the cap
> is still there, and the false beat or fuzzy tone would still exist (or
> return with the next humidity cycle).
>
>
>
> The higher percentage of false beats in the treble seems to
>
>> be indicating the smaller gauge wire cuts a deeper mark in the pin.
>>
>
> I think that the resonant frequency of the flagpoling loose (and smaller
> diameter) pin more nearly corresponds to the frequency of the treble notes,
> producing beats slow enough to hear. The false beat comes from the pitch
> difference between the vertical excursion of the string, which is solid on
> the pin, and the horizontal excursion, which is of lower pitch because of
> the flexing pin. The indication is to press against the side of the pin
> opposite the string while you play the note and observe that the beat stops,
> reappearing when the pressure is released. The string is not up the pin by
> any imaginable means, and even if it were, why does the beat stop when you
> keep the pin from flagpoling and return when you don't? It's the loose pin
> that's the real problem.
>
>
>
> I think something like epoxy or CA glue to stabilize the pins might help.
>>
>
> It most certainly does. As a less than ideal, but no other reasonable way
> out fix, I've CAd pins in place, strings on, to very good effect.
>
>
> Proper replacement of bridge pins might be necessary in some cases no
>> matter what.
>>
>
> A better fix, but I still CA or epoxy new pins in to prevent, or at least
> delay recurrence.
>
> Again, seating strings or pins doesn't fix a thing. It just gives the
> illusion, sometimes, that something positive has been done. The crushed
> bridge notch edge and the loose pin are the real problem.
>
> Ron N
>
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